1. FIELD OF THE INVENTION
This invention relates to a fuel level gauge arranged to indicate the amount of remaining fuel and provided with a remaining-amount warning apparatus for issuing a warning when the amount of remaining fuel reaches a predetermined amount.
2. DESCRIPTION OF THE RELATED ART
A known type of fuel level gauge arranged to indicate the amount of remaining fuel and provided with a remaining-amount warning apparatus for issuing a warning when the amount of remaining fuel reaches a predetermined amount comprises a scale for indicating the amount of remaining fuel on a dial, an indicating needle capable of travelling over the scale, and a warning lamp arranged to light when the amount of remaining fuel reaches a predetermined amount.
In this kind of fuel level gauge provided with a remaining-amount warning apparatus, coil means for driving the indicating needle and the warning lamp are connected to a sender secured to a fuel tank. This sender comprises a disk-shaped mounting board secured to the fuel tank, a stay secured to the frame of the mounting board, a thermistor attached to one end of the stay for detecting the amount of remaining fuel, a floating arm having a float at its distal end and rotatably secured at its proximal end to the aforesaid frame, a sliding element secured to the proximalend portion of the floating arm, and a resistance plate fixedly fitted in the frame, the sliding element sliding on the resistance plate in accordance with the floating motion of the floating arm.
The resistance plate comprises a board made of ceramics or the like, a plurality of resistors formed on the board in a printed form, and a plurality of conductive contact elements formed on the board in a printed form, one end of each of the conductive contact elements being connected to a corresponding one of the resistors and the sliding element sliding on the other ends of the conductive contact elements. One end of the resistors is connected to the coil means for driving the indicating needle, and the thermistor is connected to the warning lamp.
In the aforesaid fuel level gauge provided with such a remaining-amount warning apparatus, if the amount of remaining fuel decreases and the liquid level falls, the float descends correspondingly and the floating arm rotates downwardly. In accordance with the downward motion of the floating arm, the sliding element is caused to slide on the resistors (the conductive contact elements) to cause a variation in the resistance of the resistors. A current flowing in the coil means varies in accordance with this variation in the resistance of the resistors. Owing to the variation in the current, the composite magnetic field formed by the coil means varies so that the indicating needle travels o the scale to indicate the amount of remaining fuel.
Furthermore, if the amount of remaining fuel decreases to a predetermined amount, that is to say, if the liquid level falls to a preset position of the thermistor, the thermistor which has been immersed in the fuel is exposed to air. In consequence, the temperature of the thermistor changes and the resistance value thereof varies, thereby causing the warning lamp to light.
The fuel level gauge provided with the above-described remaining-amount warning apparatus is arranged to control a current flowing in the warning lamp by utilizing a variation which occurs in the resistance of the thermistor when the thermistor which has been placed in the fuel is exposed to air. Accordingly, it has been impossible to avoid the problems that the usable ranges of voltage and temperature are narrow and that the kinds of load resistor, warning lamp, etc. are limited since the influence of load characteristics is extremely serious.
Moreover, the operations of portions associated with an indication of the amount of remaining fuel (the floating arm, the sliding element and the resistance plate) are completely separate from those of portions associated with a warning on the amount of remaining fuel (the stay, the thermistor, etc). As a result, there is a case where an indication of the amount of remaining fuel may not accurately correspond to a warning on the amount of remaining fuel; for example, although an indication of the amount of remaining fuel represents that the amount of fuel has already decreased to a level which requires issuance of a warning, the warning lamp does not light, or although an indication of the amount of remaining fuel does not represent that the amount of fuel has decreased to a level which requires issuance of a warning, the warning lamp lights.
Moreover, since the thermistor is provided in the vicinity of the bottom of the fuel tank so that a warning can be issued when the amount of remaining fuel decreases to the minimum level, a long stay is needed, thus resulting in the problem that it is necessary to take care not to entwine the stay and the floating arm when the sender is to be mounted on the fuel tank.